Mechanical percussion mechanism

ABSTRACT

A mechanical percussion mechanism for a percussion drive of a tool insert in a handheld power tool has a rotatably supported drive shaft, a percussion body connected to the drive shaft in a manner fixed against relative rotation and supported axially movable relative to the drive shaft, a rotatably supported driven shaft connected to the drive shaft in a manner fixed against relative rotation, the percussion body having drive cams and the driven shaft having drive cams, which drive cams of the percussion body and the driven shaft are bringable into operative connection for a percussion drive of the tool insert, and an axial stop provided for the percussion body.

CROSS-REFERENCE TO A RELATED APPLICATION

The invention described and claimed hereinbelow is also described inGerman Patent Application DE 202006014850.7 filed on Sep. 27, 2006. ThisGerman Patent Application, whose subject matter is incorporated here byreference, provides the basis for a claim of priority of invention under35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to a mechanical percussion mechanism for ahandheld power tool, in particular a rotary percussion screwdriver.

From the prior art, such as German Patent Disclosure DE 10 2004 032 789A1, rotary percussion screwdrivers with a V-groove rotary percussionmechanism are known. In general, rotary percussion mechanisms convertthe continuous power output of the drive motor into a percussionlikerotary pulse, and the energy output of the motor is temporarily storedin a mass and abruptly delivered to the tool insert, such as a drillbit, by means of a pulse of high power intensity. In V-groove rotarypercussion mechanisms in particular, the rotary motion is transmitted toa weight mass (rotary percussion weight), and the rotary percussionweight is supported in such a way that an axial motion is possible. Thecontrol of the axial motion is done by V-grooves and slaving balls. Aspring assures the restoration of the rotary percussion weight.

In practice, it is found that an impact, for instance if the rotarypercussion screwdriver is unintentionally dropped, can impart such astrong impetus to the rotary percussion weight that it is displacedaxially, counter to the restoring force of the spring, so far on thedrive shaft that the slaving balls are set free and fall out of thegrooves. After that the percussion mechanism can no longer be actuated,and hence the power tool has to be replaced or repaired.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amechanical percussion mechanism which avoids the disadvantages of theprior art.

In keeping with these objects and with others which will become apparenthereinafter, one feature of the present invention resides, brieflystated, in a mechanical percussion mechanism for a percussion drive of atool insert in a handheld power tool, the mechanical percussionmechanism comprising a rotatably supported drive shaft; a percussionbody connected to said drive shaft in a manner fixed against relativerotation and supported axially movable relative to said drive shaft; arotatably supported driven shaft connected to said drive shaft in amanner fixed against relative rotation, said percussion body havingdrive cams and said driven shaft having drive cams which drive cams orsaid percussion body and said driven shaft are bringable into operativeconnection for a percussion drive of the tool insert; and an axial stopprovided for said percussion body.

The mechanical percussion mechanism according to the invention has theadvantage that even in the event of a strong impact, for instance fromunintentional or improper handling, the percussion body will not beexcessively deflected axially along the drive shaft. This isparticularly advantageous whenever the percussion mechanism, for rotaryslaving of rotationally supported components, has freely movable or inother words loose slaving elements, such as slaving balls, which couldbe set free by a strong axial displacement. The capability of axialmotion on the part of the percussion body is limited according to theinvention by the provision that the percussion mechanism is providedwith an axial stop.

The mechanical percussion mechanism of the invention serves the purposeof percussively driving a tool insert of a handheld power tool, such asa rotary percussion screwdriver. The percussion mechanism includes arotatably supported drive shaft. It further includes a percussion body,which is connected to the drive shaft in a manner fixed against relativerotation and is supported axially movably relative to the drive shaft.The percussion mechanism furthermore includes a rotatably supporteddriven shaft, which is connected to the drive shaft in a manner fixedagainst relative rotation. The percussion body has drive cams, which forthe percussive driving of the tool insert can be brought into operativeconnection with driven cams of the driven shaft. The tool insert, suchas a screwdriver bit, is located in a tool receptacle that can be drivenby the driven shaft.

The mechanical percussion mechanism is in particular a rotary percussionmechanism, and very particularly a V-groove rotary percussion mechanism.However, the invention, may also be suitable for other mechanicalpercussion mechanisms, especially other rotary percussion mechanisms.

The percussion body is connected to the drive shaft in a manner fixedagainst relative rotation, in particular via at least one slavingelement. The at least one slaving element is in particular a rollerbody, preferably a ball. The rotary slaving may be done such that eitherthe percussion body is driven by an electric motor and the rotary motionof the percussion body is transmitted to the drive shaft via slavingelements, or the drive shaft is driven by an electric motor and therotary motion of the drive shaft is transmitted to the percussion bodyby means of slaving elements. For instance, in a V-groove rotarypercussion mechanism known per se, an electric motor drives a driveshaft, which is connected to the percussion mechanism in a manner fixedagainst relative rotation via slaving balls. The slaving balls arelocated in V-grooves in the drive shaft.

The driven shaft of the percussion mechanism of the invention is alsosupported rotatably, and the driven shaft is connected to the driveshaft in a manner fixed against relative rotation. This can be done forinstance directly, by providing that the drive shaft is connected to thedriven shaft in a manner fixed against relative rotation, for instancevia a form lock. However, the rotary slaving can also be doneindirectly, by providing that as in the V-groove rotary percussionmechanism, the percussion body driven by the drive shaft transmits therotary motion to the driven shaft. This is done via the drive cam of thepercussion body and the driven cams of the driven shaft. To that end,the restoring force of a compression spring presses the percussion bodyin the direction of the driven shaft, so that the driven cams act asslaving elements.

For the percussive drive of the tool insert, the percussion body isadditionally supported axially movably on the drive shaft. A restoringelement, preferably a compression spring, for instance in the form of ahelical spring, is also provided, which keeps the percussion bodyprestressed. Depending on the construction of the mechanical percussionmechanism, the percussion body may be prestressed either in thedirection of the driven shaft or in the direction of the drive motor.For instance, in a V-groove rotary percussion mechanism known per se,the percussion body is prestressed in the direction of the driven shaftby a helical spring, as a restoring element.

The drive end of the helical spring is located for instance on thehousing of the drive motor or the end plate of a bearing for the driveshaft. The mode of operation of a mechanical percussion mechanism, andin particular how the drive cams can be operatively connected to thedriven cams of the drive shaft for the percussive drive of a tool insertby means of a longitudinal motion of the percussion body so that energycan be transmitted via the drive cams to the driven cams, is familiar toone skilled in the art and will therefore not be described in detailhere.

In a preferred embodiment, the stop is embodied as a spring element. Thespring element is preferably formed from an elastic material, inparticular an elastomer, such as rubber or soft foam. However, thespring element may also be a spring, such as a helical spring or cupspring, of metal or plastic. A spring element as a stop has theadvantage that the axial motion of the percussion body is not merelylimited by the stop but also damped.

The stop is also preferably embodied annularly or in disklike form. Inparticular, the stop is displaced annularly or in disklike form aroundthe drive shaft. The annular or disklike stop is then preferablysupported on the drive shaft. For instance, it may be slipped onto thedrive shaft and optionally glued there.

Because of the annular or disklike embodiment of the stop, particularlyas an annular or disklike spring element, the largest possible area ofthe percussion body comes into contact with the stop when the percussionbody meets the stop, and thus the stop can damp the axial motionespecially well.

In an embodiment of the mechanical percussion mechanism of the inventionin which the percussion body is prestressed in the direction of thedriven shaft via a restoring element, the axial stop prevents excessiveaxial deflection of the percussion body in the direction of the drivemotor. Accordingly, in this embodiment, the stop is located in theregion of the drive end of the drive shaft. In the alternativeembodiment in which the percussion body is prestressed in the directionof the drive motor, the axial stop prevents an excessive deflection ofthe percussion body in the direction of the driven shaft. For thatpurpose, the stop is located in the region of the driven end of thedrive shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the drive train of a handheld power tool in accordance withthe present invention, with a mechanical rotary percussion mechanism, inan exploded view; and

FIG. 2 is a cross section through the mechanical rotary percussionmechanism of FIG. 1 in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the exploded view of FIG. 1, the drive train of a rotary percussionscrewdriver is shown, with a mechanical percussion mechanism 50.Hereinafter, only the essential components will be discussed.

An electric motor 10 (shown schematically) includes an armature shaft12, on which a gear wheel, serving as a drive pinion 31, is located, ina manner fixed against relative rotation. The drive pinion 31 forms onepart of a two-stage planetary gear 30 and drives planet wheels 32 withthe first gear stage. The planet wheels 32 roll inside a ring gear 36.As a result, a first sun wheel 33 is rotated, which in turn, via a setof teeth 34, drives further planet wheels 35 of the second gear stage.The planet wheels 35 roll inside the ring gear 36 and drive a second sunwheel 37. The second sun wheel 37 is connected to the drive shaft 51 ofthe mechanical percussion mechanism 50 in a manner fixed againstrelative rotation.

To that end, in FIG. 1, the sun wheel 37 is embodied in the form of pinsin one piece with the drive shaft 51. The drive shaft 51 is supported,on its end toward the gear, in a bearing 52, preferably a rollerbearing, in particular a deep-groove ball bearing. The two-stageplanetary gear 30, the bearing 52, and part of the drive shaft 51 arereceived in a separate housing 20 of plastic. On the gear end, thehousing 20 is provided with a cap, also of plastic, as a cover element22. The cover element 22 has a central opening 23 for receiving thearmature shaft 12. On the diametrically opposed end, the bearing end, ofthe housing 20, the drive shaft 51 protrudes out of the housing 20.

The mechanical percussion mechanism 50 of FIG. 1 is a V-groove rotarypercussion mechanism. It includes a rotatably supported drive shaft 51with slaving elements 57 in the form of slaving balls in a V-groove 58.Via the slaving elements 57, a percussion body 56 is connected to thedrive shaft 51 in a manner fixed against relative rotation, so that thedrive shaft 51, driven by the electric motor 10 via the planetary gear30, sets the percussion body into rotary motion. Simultaneously, thepercussion body 56 is axially movably supported on the drive shaft 51.The percussion body 56 has drive cams 53. Via the percussion body 56with the drive cams 53, a rotatably supported driven shaft 59 isconnected to the drive shaft 51 in a manner fixed against relativerotation via driven cams 54.

In nonpercussive driving, the percussion body 56 is prestressed in thedirection of the driven shaft 59 via a compression spring 55. Then thedrive cams 53 engage the driven cams 54 in such a way that the rotarymotion of the percussion body 56 is transmitted to the driven shaft 59.The driven shaft 59 is likewise supported in a bearing 61. A shim 24serves to receive and fix the compression spring 55 and also to protectthe housing 20 against heating and wear from the friction of thecompression spring 55. For receiving a tool insert (not shown), thedriven shaft 59 is connected to a tool receptacle 62. The percussionmechanism 50 is received in a housing part 63, preferably of metal. Ahousing screen 64 of an elastic plastic covers at least some of thehousing part 63.

The mode of operation of a V-groove rotary percussion mechanism will notbe discussed in detail here, since it is familiar enough to one skilledin the art. As to the mode of operation, it will merely be indicatedthat by means of a screw (not shown) contacting a workpiece, the torquedemand increases abruptly, and the rotary motion of the driven shaft 59is blocked. The percussion body 56 driven by the drive shaft 51continues to rotate and is pressed by the slaving elements 57 in theV-shaped grooves 58 in the direction of the drive end of the drive shaft51, counter to the restoring force of the compression spring 55. In theprocess, the drive cams 53 of the percussion body 56 meet the drivencams 54 of the driven shaft 59, and the energy of the percussion body56, stored as a result of the rotation, is therefore transmitted to thedriven shaft 59. As a result of this longitudinal motion, the drive cams53 slip farther on the driven cams 54 and slide past them.

For the sake of greater simplicity, the mechanical percussion mechanism50 is shown in FIG. 1 without a stop. However, in the cross section ofFIG. 2 an axial stop 70 can be seen clearly. In the embodiment of FIG.2, the axial stop 70 is formed by an annular or disklike spring elementmade from an elastomer. The diameter of the disklike elastomer springelement is less than the diameter of the compression spring 55, and thusthe stop 70 can be located inside the compression spring 55. The stop 70is supported on the drive shaft 51 in a manner fixed against relativerotation and rests on the shim 24. As a result, the maximum axialdeflection of the percussion body 56 on the drive shaft 51 counter tothe compression force of the compression spring 55 is limited in thedirection of the drive end of the drive shaft 51.

Without an axial stop 70, the percussion body 56 could be moved stillfarther axially in the direction of the drive end of the drive shaft 51,so that the slaving elements 57 could be set free and fall out of theV-grooves 58.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the type described above.

While the invention has been illustrated and described as embodied in amechanical percussion mechanism, it is not intended to be limited to thedetails shown, since various modifications and structural changes may bemade without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

1. A mechanical percussion mechanism for a percussion drive of a toolinsert in a handheld power tool, the mechanical percussion mechanismcomprising a rotatably supported drive shaft; a percussion bodyconnected to said drive shaft in a manner fixed against relativerotation and supported axially movable relative to said drive shaft; arotatably supported driven shaft connected to said drive shaft in amanner fixed against relative rotation, said percussion body havingdrive cams and said driven shaft having drive cams, which drive cams onsaid percussion body and said driven shaft are bringable into operativeconnection for a percussion drive of the tool insert; and an axial stopprovided for said percussion body.
 2. A mechanical percussion mechanismas defined in claim 1, wherein said stop for said percussion body isconfigured as a spring element.
 3. A mechanical percussion mechanism asdefined in claim 1, wherein said stop for said percussion body iscomposed of an elastic material.
 4. A mechanical percussion mechanism asdefined in claim 3, wherein said stop for said percussion body iscomposed of an elastomer.
 5. A mechanical percussion mechanism asdefined in claim 1, wherein said stop for said percussion body isconfigured as an annular stop.
 6. A mechanical percussion mechanism asdefined in claim 5, wherein said annular stop is supported on said driveshaft.
 7. A mechanical percussion mechanism as defined in claim 1,wherein said percussion body is connected to said drive shaft in amanner fixed against relative rotation via at least one slaving element.8. A mechanical percussion mechanism as defined in claim 7, wherein saidat least slaving element is configured as a roller body.
 9. A mechanicalpercussion mechanism as defined in claim 8, wherein said at least oneslaving element is configured as a ball.
 10. A handheld power tool,comprising a tool insert which is percussively driven; and a mechanicalpercussion mechanism for a percussive drive of said tool insert, saidmechanical percussion mechanism including a rotatably supported driveshaft, a percussion body connected to said drive shaft in a manner fixedagainst relative rotation and supported axially movable relative to saiddrive shaft, a rotatably supported driven shaft connected to said driveshaft in a manner fixed against relative rotation, said percussion bodyhaving drive cams and said driven shaft having drive cams, which drivecams of said percussion body and said driven shaft are bringable intooperative connection for the percussion drive of said tool insert, andan axial stop provided for said percussion body.